try Flipping "L.A. Is My Lady" by Frank Sinatra and Quincy and see if you still believe that
There isn't any. All genres are great for sampling though it depends on how trained your ear is on finding parts in a mix. 60's or 70's rock are good for guitar and bass sounds. I think most people using rock records are after drumbreaks. Several years ago i was heavy digging for rock records because every i found had a kick, snare or some sort of drumbreak on it.
You'd say Hawaiian records are crap but who knows? The next person might dig it, others don't.
its just that i dont like the jazzy feeling that often transfers to the hiphop track when sampling jazz. And the fact that so many ppl sample it so its harder to find unused samples compared to other genres